（1）(a+b+c)(c-a-b)
=c^2-(a+b)^2
=c^2-a^2-2ab-b^2
（2）（x^2-x-1）^2
=x^4-2x^2(x+1)+(x+1)^2
=x^4-2x^3-2x^2+x^2+2x+1
=x^4-2x^3-x^2+2x+1
(3)(2x-y-z)^2
=4x^2-4x(y+z)+(y+z)^2
=4x^2-4xy-4xz+y^2+2yz+z^2
如果本题有什么不明白可以追问,